The conventional method of laundering textiles, used by United States consumers in the home, is carried out by placing from about 5 pounds to about 8 pounds of textiles into a top loading washing machine which typically uses about 45 gallons of water. Detergent is added to the machine in an amount determined by the manufacturer to provide the best cleaning results for a specified amount of textiles and volume of water. The water and detergent form what is referred to as the wash liquor. Soil is removed from the textiles and suspended in the wash liquor by mechanical agitation. At the end of the washing cycle, the wash liquor is drained from the wash basket and the textiles are rinsed with water. Additional mechanical agitation, which occurs during the rinse cycle, removes the detergent residue from the textiles. After the rinse water is drained from the wash basket, a high speed spin of the wash basket removes most of the water from the textiles.
A number of features of the conventional washing method could be improved to provide better consumer satisfaction with the process itself and the results obtained. For example, the changing of one feature, the amount of water used in the wash process, would result in a sizable cost savings to the consumer. It is well-established that the largest single factor effecting the consumer's cost per wash load is the amount of energy used to heat the water used in the washing cycle. Accordingly, it would be desirable to modify existing washing processes to consume less energy, and therefore result in a lower cost to the consumer. One such convenient way in which this can be accomplished is to reduce the amount of water consumed in the process. Appliance or washing machine manufacturers responding to this need for a washing machine have developed so-called "low water" washing machines which use about 25 gallons of water for each wash and rinse cycle or 40% less water than conventional top loading washing machines. However, for maximum cleaning benefits, the detergent used in such low water washing processes must be tailored to the machine operating conditions. Currently available detergent compositions are not optimized to deliver superior cleaning results in the newly developed low water wash systems.
During the mechanical agitation phase of a normal wash cycle, surfactants in the detergent composition can produce an excessive amount of foam, reducing the quality of the washing process. Where a reduced amount of water is used in the washing process, currently available detergent compositions almost always produce unacceptably large amounts of foam which are found aesthetically objectionable to consumers and which can reduce the level of cleaning resulting from the conventional washing process. The solution to the problem of excessive foaming lies in the use of nonionic surfactants in laundry detergent compositions since, as a group, the nonionics do not have the foaming power of anionic surfactants.
Nonionic surfactants are well suited to formulation in laundry detergents since their hydrophilic group is chemically inert and they can be made compatible with many different types of builders. Detergent compositions which include nonionic surfactant generally require high concentrations in the wash for a significant benefit, as opposed to compositions comprising mainly anionics which are usable at lower concentrations. The high concentrations of nonionic surfactant necessary for the production of significant benefits are attainable in the low water wash systems described herein.
The laundry detergent compositions described herein and composed of high amounts of nonionic surfactants exhibit superior cleaning performance, over conventional detergents used in low water wash systems, because the detersive surfactant is partially colloidal and present as micelles. In conventional liquid detergents, which contain a high concentration of anionic surfactants, the detersive surfactant species exist mainly as monomers. Conventional detergent solutions containing a large proportion of monomeric surfactant species have long been selected by workers in the art for use in washing because they act much faster, under prior art conditions, than highly micellized solutions. However, these monomeric solutions are not satisfactory in a low water wash system where the most effective cleaning can only result if the water and surfactant phases separate. In conventional washing processes, separation of the water and surfactant phases is prevented by the presence of fatty acids from soiled fabrics in the wash liquor. Furthermore, current detergent formulations do not adequately separate during low water wash processes so as to provide effective cleaning and prevent redeposition. This problem is exacerbated further when the low water wash process is operated at relative low temperatures (i.e., less than about 25.degree. C.) as is typical in many countries such as the United States of America and Japan.
The emulsified laundry detergent compositions described herein solve the problem of ineffective cleaning which results from the use of monomeric surfactant species in a low water wash system by providing for separation of the surfactant and water phases before and during cleaning. As a result of the separation, the resulting surfactant-rich phase, which consists of elongated rod-like micelles, directly interacts with the surface of the clothes and modifies the soil to produce superior cleaning. The subsequent rinse removes the soil from the substrate and the soil is solubilized in an emulsion, thus preventing redeposition.
The emulsified laundry detergent compositions described herein solve the problem of excessive amounts of suds formed during the washing process. In the past, detergent compositions used in machines employing low water wash processes included higher levels of relatively expensive suds suppressors which obviously increased the cost of the detergent product. Thus, it would be desirable to have a detergent composition specifically tailored for low water wash machines which provides superior cleaning at low washing temperatures without the need for high levels of expensive suds suppressors.
Accordingly, despite the aforementioned disclosures in the art, the need exists for a commercially available detergent composition which exhibits superior cleaning in laundry machines employing low water wash processes, especially at low wash water temperatures. There is also a need for a detergent composition which provides such superior cleaning without the need for high levels of suds suppressors. Furthermore, despite disclosures in the detergency art of detergent compositions comprising a nonionic surfactant, strong electrolyte and builder, used in a washing liquor where the surfactant coexists in a single phase with water, the need exists for an emulsified detergent composition which provides for a phase separation mechanism of soil removal over a broad washing temperature range.